Snapshots in Neuroscience: Rat dorsal hippocampus

These images have been selected to showcase the art that neuroscience research can create.

As described by the authors: “This vibrant fluorescence image presents a high-resolution coronal section of the rat hippocampus, a brain region pivotal to memory and spatial navigation. At the center of the image, the hippocampus exhibits a beautifully folded arrangement (dark green): The horizontal V-shaped fold of the dentate gyrus is embraced by the overarching arch of the Cornu Ammonis (CA) region, which is anatomically divided into CA3, CA2, and CA1. Notably, this snapshot features vivid orange vertical tracks piercing through these neural layers. These are the paths of silicon probes used to record neural activity in the dorsal CA1 (dCA1).

“While the dCA1 is traditionally associated with spatial navigation and the formation of contextual memories, recent research suggests that it also contributes to value-based decision-making and goal-directed behavior by integrating complex information into flexible, behaviorally relevant representations. In our paper, we explored how reward information, such as the memory of a "success" or "failure," is refined across multiple brain regions, including the dCA1. We found that while other brain regions, such as the motor cortex, hold a somewhat ambiguous representation of rewards, the dCA1 "binarizes" this information into crystal clear categories. Recognizing the unique functional roles of the hippocampal subregion helps us better understand how the brain might transform the multifaceted stream of everyday behavior into the discrete, meaningful labels that define our memories and future decisions

"This image was captured using a wide-field fluorescence microscope (Olympus BX51) at 4x magnification. The 50-μm–thick coronal section was obtained from a channelrhodopsin-2 (ChR2)-expressing transgenic (Thy1-ChR2-Venus) rat. These rats abundantly express the ChR2-Venus fusion protein in cortical and other neurons under the control of the Thy1.2 promoter, vividly revealing the distinct laminar organization and density of the hippocampal subfields. The electrode tracks were visualized using DiI."

“The image was taken using a Nikon confocal microscope with a 20x objective.”

This fluorescence image features the dorsal hippocampal region (dark green) of a Thy1-ChR2-Venus transgenic rat, with DiI-labeled tracks (orange) marking the path of silicon probes into the CA1 region of the hippocampus. Image credit: Shogo Soma.

Read the full article:

Hierarchical distribution of reward representation in the cortical and hippocampal regions
Shogo Soma, Masahiro Okamoto, Yui Mimura, and Yoshikazu Isomura